Generally, in control of an AC rotating machine, in order to supply current with an appropriate phase corresponding to the rotational position of a rotor, a rotational position sensor such as an encoder, a resolver, or a Hall element is needed.
Therefore, when the rotational position sensor is abnormal, the AC rotating machine cannot be controlled, and thus it is necessary to stop an AC rotating machine.
From this viewpoint, the following technology is proposed. When the rotational position sensor is abnormal, the rotational position of the rotor is estimated without using the rotational position sensor, and a rotational position signal (hereinafter, referred to as a control angle) for controlling the AC rotating machine is switched to the estimated rotational position, thus continuing control of the AC rotating machine even when the position sensor is abnormal.
For example, in a conventional AC rotating machine control device described in Patent Document 1, when a rotational position sensor is abnormal, high-frequency limitation voltage for estimating the rotational position is applied to windings of an AC rotating machine, and on the basis of the corresponding current detected value from the AC rotating machine, the AC rotating machine is controlled without using a rotational position sensor.
Since a certain time is needed for estimating the rotational position, in a rotational position uncertain period which arises in shifting to sensorless control in which the AC rotating machine is controlled on the basis of the estimated rotational position, a rotational position obtained from an output signal of the rotational position sensor immediately before the shifting to sensorless control is used for the sensorless control during a period immediately after the shifting to sensorless control, thus solving the problem.
Here, abnormalities in the rotational position sensor include abnormality of the rotational position sensor itself, and disconnection abnormality of a signal line or a feed line of the rotational position sensor.